Tofu

Tofu, also called bean curd, is a food made by coagulating soy milk and then pressing the resulting curds into soft white blocks. It is a component in many East Asian and Southeast Asian cuisines. There are many different varieties of tofu, including fresh tofu and tofu that has been processed in some way. Tofu has a subtle flavor and can be used in savory and sweet dishes. It is often seasoned or marinated to suit the dish.

Tofu originated in ancient China some 2,000 years ago. Chinese legend ascribes its invention to prince Liu An. Tofu and its production technique were introduced into Korea and then Japan during the Nara period. It spread into other parts of East Asia as well. This spread likely coincided with the spread of Buddhism because it is an important source of protein in the vegetarian diet of East Asian Buddhism. Li Shizhen in the Ming Dynasty described a method of making tofu in Bencao Gangmu.

Tofu has a low calorie count, relatively large amounts of protein, and little fat. It is high in iron and depending on the coagulant used in manufacturing, may also be high in calcium or magnesium.

Production

Tofu is made by coagulating soy milk and pressing the resulting curds. Although pre-made soy milk may be used, some tofu producers begin by making their own soy milk, which is produced by soaking, grinding, boiling and straining dried (or, less commonly, fresh) soybeans.

Coagulation of the protein and oil (emulsion) suspended in the boiled soy milk is the most important step in the production of tofu. This process is accomplished with the aid of coagulants. Two types of coagulants (salts and acids) are used commercially. The third type of coagulant, enzymes, is not yet used commercially but shows potential for producing both firm and "silken" tofu.

Varieties

There is a wide variety of tofu available in both Western and Eastern markets. Despite the large variety, tofu products can be split into two main categories: fresh tofu, which is produced directly from soy milk, and processed tofu, which is produced from fresh tofu. Tofu production also creates important side products which are often used in various cuisines.

Fresh tofu

Depending on the amount of water that is extracted from the tofu curds, fresh tofu can be divided into three main varieties. Fresh tofu is usually sold completely immersed in water to maintain its moisture content.

Soft tofu

Soft/silken tofu is undrained, unpressed tofu that contains the highest moisture content of all fresh tofus. Silken tofu is produced by coagulating soy milk without curdling it. Silken tofu is available in several consistencies, including "soft" and "firm", but all silken tofu is more delicate than regular firm tofu (pressed tofu) and has different culinary uses. In Japan and Korea, traditional soft tofu is made with seawater.

Firm tofu

Although drained and pressed, this form of fresh tofu still contains a great amount of moisture. It has the firmness of raw meat but bounces back readily when pressed. The texture of the inside of the tofu is similar to that of a firm custard. The skin of this form of tofu has the pattern of the muslin used to drain it and is slightly more resilient to damage than its inside. It can be picked up easily with chopsticks.

Extra firm tofu

Extra firm tofu (literally "dry tofu" in Chinese) is an extra firm variety of tofu where a large amount of liquid has been pressed out of the tofu. Dòu gān contains the least amount of moisture of all fresh tofu and has the firmness of fully cooked meat and a somewhat rubbery feel similar to that of paneer.

Processed tofu

Many forms of processed tofus exist, due to the varied ways in which fresh tofu can be used. Some of these techniques likely originate from the need to preserve tofu before the days of refrigeration, or to increase its shelf life and longevity. Other production techniques are employed to create tofus with unique textures and flavors.